The present invention relates to a hydraulically operated pressure element for forcing contacts against electrodes in electrofurnaces and in a particular position under utilization of a cooled carrier ring circumscribing the respective electrodes, and being provided for carrying an extensible bushing.
Such a bushing is, for example, made of a cover fastened to the carrier ring, and another cover is disposed adjacent respective contacts with corrugated bellows interposed between the two covers; a hydraulic pressure medium forces the contact carrying cover under utilization of the extensibility of the bellows against the electrodes to ensure contact making.
Devices of the type referred to above are generally known. It was found, however, that the particular constructions used in the prior art are deficient in that a complete filling of the interior of the bellows through the hydraulic medium is not assured. Rather, air bubbles or an air cushion can remain which modifies the force relationships, and particularly the relationship between the pressure of the hydraulic medium as applied on one hand, and the force of contact making with the electrode on the other hand.
Such an air cushion can particularly arise during decompression and emptying of the interior cavity of the bellows as air may be sucked into the emptying space. Thus, the effective requirement for such a device to work with sufficient accuracy, namely, incompressibility or de facto incompressibility of the pressure medium, is no longer present. This of course may entail an interference with the function of the electrode clamping.
Another aspect to be considered is that the known bellows being used for the stated purpose are really of a relatively short life for reasons of inadequate resistance against corrosion due to the particular environment in which they have to operate which has, by necessity, certain chemically aggressive medium. To some extent related to this aspect, but from a different point of view quite independently therefrom, is another drawback of the known bellows, in that for reasons of manufacturing tolerances relatively large differences in the axial spring forces of the different bellows had been observed.
Another aspect to be considered is that the known bellows, and particularly in dependency upon their weight, i.e., of their mass involved, there is a certain reduction in wattless currents on account of modification in the induction of the electric current involved whenever the bellows expand or contract.